1. Field of the Invention
The invention relates to a multi-needle recording head adapted to be used for electrostatic recording and to a method of manufacturing such multi-needle recording head. More particularly, the invention is directed to an improved multi-needle recording head formed by fixing two staggered arrays of recording electrode wires arranged at a predetermined pitch by an electrically insulating electrode support block and to an improved method of manufacturing such multi-needle recording head by fixing the recording electrode wires while wound around a winding jig, and the present invention relates to a molding apparatus used for manufacturing a multi-needle recording head adapted to be used for electrostatic recording. More particularly, the invention is directed to an improved structure for supporting control electrodes within cavity grooves of a mold into which an electrically insulating resin is charged.
2. Related Art
A multi-needle recording head used for electrostatic recording is generally formed so that a first array of recording electrodes consisting of N blocks of wires, each block including M wires and a second such array of recording electrodes are arranged at a high density at a predetermined pitch. The second array of recording electrodes are disposed in parallel with the first array of recording electrodes at a predetermined distance from the first array of recording electrodes. These recording electrodes are fixed by an electrode support block made of an electrically insulating resin so that the respective end faces of the recording electrodes are exposed.
A method of manufacturing the thus constructed multi-needle recording head has already been disclosed by the inventors (Japanese Patent Unexamined Publication No. 2-239953). The method is such as efficiently producing the multi-needle recording heads using two winding jigs 301 such as shown in FIG. 6. This winding jig 301 includes: cavity grooves 305 into which an electrode-support-block-forming resin is charged with control electrodes 100 set; wire retaining grooves 309, formed at projections 306, 307, 308 on the edges of the cavity grooves 305 so as to traverse the cavity grooves 305, for allowing recording electrode wires 200 to be arranged at a predetermined pitch; and directing pins 302, binding pins 303, and turn pins 304 that allow the wires 200 to be hooked and wound in an arbitrary direction and at an arbitrary position on both side wall surfaces of the winding jig 301. A single recording electrode wire is continuously wound by alternately twisting the wire on the pins 302, 303, 304 so as to traverse the cavity grooves 305 after the control electrodes 100 have been set in the cavity grooves 305 of the winding jig 301, and M.times.N recording electrode wires 200 are stretched over the cavity grooves 305 at a predetermined pitch by binding the wires every block of recording electrodes.
The winding of a wire 200 around the winding jig 301 is mechanically done in the following way. The wire 200 is paid off from a nozzle 312 of a wire supply unit 310 while given some tension by a not shown back tension mechanism utilizing both a reciprocal linear motion along the axis of a wire guide means 311 (in the direction indicated by the arrows) and oscillation or rotation of the winding jig 301, and hooked on the predetermined pins 302, 303, 304, and wire retaining grooves 309, . . . , 309. The thus prepared winding jig 301 is set end-to-end with the other winding jig (not shown) similarly prepared with the second array of recording electrodes and control electrodes set. Then, the resin is charged into a space formed between the cavity grooves 305, 305 of the two butted winding jigs 301, 301 to form the electrode support block. In the middle of the space formed between the cavity grooves 305, 305 are wires 200, 200 forming the first and second arrays of recording electrodes and the corresponding control electrodes 100,100. These wires 200,200 and control electrodes 100, 100 are disposed in parallel with each other under a predetermined positional relationship. The electrode-support-block-forming resin is charged into the periphery of these wires 200 and electrodes 100. After the electrode support block has been solidified, a bundle of wires 200 is taken out of the turn pins 304, and the multi-needle recording heads are taken out of the winding jigs 301, 301.
Further, this conventional winding method addresses another problem. That is, even if the wires are wound in parallel at a predetermined pitch so as to traverse the cavity grooves 305, when the resin is charged into the space formed between the two cavity grooves 305, 305 by placing the two winding jigs 301, 301 with windings end-to-end to form the electrode support block, the recording electrode wires 200 slacken due to linear expansion caused by the heating involved in the hardening of the resin or the like. Further, in the case of using a thermosetting resin as the electrically insulating resin and heating the winding jigs 301, 301 after the resin has been charged, the wires likewise slacken due to heat. That is, if the width of the cavity groove 305 between the wire retaining grooves 309,309 on the projections 306 and 307 or 306 and 308 on both sides of the cavity groove which retain the recording electrode wires 200 is large, the linear expansion of the recording electrode wires 200 due to heat produced by the electrically insulating resin becomes so affecting as not to be neglected, causing such a level of slackening as shown in FIG. 4(C). Still further, this slackening may accompany such a displacement of the recording electrode wires 200 as shown in FIG. 4(B) by intimate contact between wires due to the flow or surface tension of the resin even if the recording electrode wires 200 have been wound correctly.
Since such slackening and displacement from grooves of the recording electrode wires cause serious electrode performance defects such as defective linearity, defective pitch, and defective shortcircuiting of the recording electrodes such as shown in FIGS. 5(B) and (C), an improvement in the conventional winding method has been called for.
However, in the case of forming the mold 301 by using an extruded aluminum member, relatively thin projecting portions, particularly, the projections 306, 307, 308 outside the cavity grooves 305 tend to produce under cut portions with inward deformation. If the control electrode support plates 314, 315 are arranged along the projections 306, 307, 308 to overcome this problem, it becomes sometimes difficult to take out the multi-needle recording head from the mold 301 after both the control electrodes 102a, 102b and the wires 310 forming the recording electrodes have been fixed by charging the resin into the cavity grooves 305.